1. Field of the Invention
The present invention relates generally to a small gas turbine engine, and more specifically to a swirl combustor.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a gas turbine engine, a compressor supplies compressed air into a combustor, a fuel is burned in the combustor to produce a hot gas flow, and the hot gas flow is passed through a turbine to drive the compressor. In a small engine, swirl combustors are used to burn the fuel in a small combustor space. A typical straight-though combustor, like those found on larger engines, burn the fuel along a straight path through the combustor. In a small engine, the combustor space is limited. Thus, swirl combustors increase the distance in which the fuel particles can travel within the combustor without increasing the axial length of the combustor.
One major problem with small swirl combustors is igniting the fuel. A swirl combustor will also produce a very fine mist of fuel particles that can burn completely in a shorter travel distance within the combustion zone. The fine atomization of the fuel in a rotary cup fuel injector will produce a fine fuel mist 10 times that of a fuel injector nozzle. The U.S. Pat. No. 6,983,606 B2 issued to Brown on Jan. 10, 2006 discloses a rotary cup combustor for a small gas turbine engine, and is herein incorporated by reference.
In a swirl combustor, another major problem is in the initial ignition of the fuel to start the engine. A swirl combustor produces a high velocity air flow into the combustor that can blow out any flame used to ignite the fuel and air mixture. In the past, pyrotechnic igniters have been used that produce an explosion to ignite the fuel and air mixture. However, pyrotechnic igniters are expensive and add considerable weight. Glow-plugs are used to start hobby-type gas turbine engines because they are cheap. However, glow plugs stay on continuously and therefore do not last long. Fuel nozzles are also expensive and can easily clog. Together, fuel nozzles and pyrotechnic igniters can account for 40% or more of the overall cost of a small gas turbine engine.